The present invention relates to flooring systems designed to reduce sound transmission, and more specifically relates to an improved nonwoven mat which improves acoustical isolation while avoiding potential moisture retention occurring in some conventional poured underlayment installations.
Conventional flooring systems include a subfloor of poured concrete or plywood. Various combinations of sound mats and underlayments located between the subfloor and the finished floor (typically ceramic tile, vinyl tile or hardwood) have been used to reduce sound transmission.
Sound rated or floating floor systems are known for acoustically isolating a room beneath a floor on which impacts may occur, such as pedestrian footfalls, sports activities, dropping of toys, or scraping caused by moving furniture. Impact noise generation can generally be reduced by using thick carpeting, but where vinyl, linoleum, tile, hardwood, wood laminates and other types of hard surfaces including decorated concrete finishes are to be used, a sound rated floor is desirable and required by codes for acoustical separation of multifamily units. The transmission of impact noise to the area below can be reduced by resiliently supporting or acoustically decoupling and/or dampening the underlayment floor away from the floor substructure. The entire floor system contributes to transmitting the noise into the area below. If the floor surface receiving the impact is isolated from the substructure, then the impact sound transmission will be greatly reduced. A dampening material can also reduce transmitted noise. Likewise, if the ceiling below is isolated from the substructure, the impact sound will be restricted from traveling into the area below.
Sound rated floors are typically evaluated by American Society for Testing and Materials (ASTM) Standards E90 for Sound Transmission Class (STC) ratings and E492 with respect to Impact Insulation Class (IIC). The greater the IIC rating, the less impact noise will be transmitted to the area below. The greater the STC rating, the less airborne sound will be transmitted to the area below. The International Building Code (IBC) specifies that floor/ceiling installations between units on multi-family buildings must have an IIC rating of not less than 50 and an STC rating of not less than 50. Even though an IIC rating of 50 meets many building codes, experience has shown that in luxury condominium applications floor-ceiling systems having an IIC of less than 55 may not be acceptable because some impact noise is still audible and considered annoying at those levels.
Conventional floor systems may employ a poured underlayment located between the finished floor and the subfloor, typically for providing a smooth, monolithic substrate for the finished floor. A suitable poured underlayment is LEVELROCK® floor underlayment sold by United States Gypsum Company of Chicago, Ill. (USG). LEVELROCK® underlayment is a mixture of Plaster of Paris, Portland Cement and Crystalline Silica. The underlayment is part of a floor system that also may include a fabric, polymer or combination of both or rubber-like mat which provides sound isolation. Several manufacturers of drainage mats and sound mats manufacture entangled mats that can be utilized for sound isolation (IIC and STC) for floor/ceiling assemblies. These mats are typically sandwiched between the subfloor and a poured floor underlayment, and typically involve a matrix of various petrochemical materials, such as nylon, polypropylene, or polyethylene with some type of backing. The function of the backing is to provide a platform upon which the underlayment is poured.
There are concerns that these backings may leak water into the cavity with negative consequences. One potential issue is that excess water in the poured underlayment slurry prior to setting provides moisture that can encourage the growth of mold and mildew; second is that moisture can affect some materials like nylon and be absorbed by the polymer, causing it to change dimension. When this dimensional change takes place, the result is often lipping at seams and can cause subsequent cracking issues within the underlayment itself.
Because the backings on current mats in the marketplace tend to be thin, there is little or no contribution to the sound attenuation performance of the sound mat. The IIC and STC performance of the sound mat is achieved through a decoupling effect.